bazel support for tools (#982)

* packages versions updated to be in sync with modern python versions

WORKSPACE

@@ -34,3 +34,16 @@ new_local_repository(
     build_file = "@//bindings/python:python_headers.BUILD",
     path = "/usr/include/python3.6",  # May be overwritten by setup.py.
 )
+
+http_archive(
+    name = "rules_python",
+    url = "https://github.com/bazelbuild/rules_python/releases/download/0.1.0/rules_python-0.1.0.tar.gz",
+    sha256 = "b6d46438523a3ec0f3cead544190ee13223a52f6a6765a29eae7b7cc24cc83a0",
+)
+
+load("@rules_python//python:pip.bzl", pip3_install="pip_install")
+
+pip3_install(
+   name = "py_deps",
+   requirements = "//:requirements.txt",
+)

requirements.txt

@@ -0,0 +1,2 @@
+numpy == 1.19.4
+scipy == 1.5.4

tools/BUILD.bazel

@@ -0,0 +1,19 @@
+load("@py_deps//:requirements.bzl", "requirement")
+
+py_library(
+    name = "gbench",
+    srcs = glob(["gbench/*.py"]),
+    deps = [
+      requirement("numpy"),
+      requirement("scipy"),
+    ],
+)
+
+py_binary(
+    name = "compare",
+    srcs = ["compare.py"],
+    python_version = "PY2",
+    deps = [
+        ":gbench",
+    ],
+)